Air-cooled heat exchanger and system and method of using the same to remove waste thermal energy from radioactive materials

ABSTRACT

A system for removing thermal energy generated by radioactive materials is provided. The system comprises an air-cooled shell-and-tube heat exchanger, comprising a shell and plurality of heat exchange tubes arranged in a substantially vertical orientation within the shell, the heat exchange tubes comprising interior cavities that collectively form a tube-side fluid path, the shell forming a shell-side fluid path that extends from an air inlet of the shell to an air outlet of the shell, the air inlet at a lower elevation than the air outlet; a heat rejection closed-loop fluid circuit comprising the tube-side fluid path, a coolant fluid flowing through the heat rejection closed-loop fluid circuit, the heat rejection closed-loop fluid circuit thermally coupled to the radioactive materials; and the air-cooled shell-and-tube heat exchanger transferring thermal energy from the coolant fluid flowing through the tube-side fluid path to air flowing through the shell-side fluid path.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/478,788, filed Apr. 25, 2011, the entirety of whichis incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to air-cooled heat exchangersand systems and methods of using the same to remove thermal energy fromradioactive materials, and specifically to air-cooled heat exchangersand systems and methods of using the same to remove waste thermal energyfrom radioactive materials, such as waste thermal energy of spentnuclear fuel.

BACKGROUND OF THE INVENTION

The reactor vessel and the spent fuel pool in nuclear power plants areprincipal locations of heat generation during the plant's operation orsubsequent to a scram. In lightwater reactor installations, the heatproduced in a reactor even after shutdown can be as much as 8% of thereactor's thermal power at the beginning of the scram decayingexponentially to less than 1% of the operating thermal power in a day'stime. The heat energy produced by the irradiated nuclear fuel isdeposited in the body of water surrounding the fuel in both the reactorand the fuel pool. Nuclear power plants are equipped with multiplesystems to transfer the energy from the heated water mass (which istypically contaminated by traces of radionuclides) to a clean water loop(sometimes referred to as the component cooling water) using ashell-and-tube heat exchanger. The heat collected by the “componentcooling water” is in turn rejected to the plant's natural heat sink suchas a lake, a river, or an ocean through another tubular heat exchanger.The use of a closed loop component cooling water system to deliver thenon-beneficial heat generated inside the nuclear plant (i.e., heat thatcannot be harnessed as productive energy) to the aqueous environment hasbeen the universal means of removing heat from the (potentiallycontaminated) fuel-exposed water in a nuclear plant. However, the recentdevastating tsunami in the wake of the massive earthquake in the PacificOcean that struck Fukushima Daiichi plants in Japan showed thevulnerability in the state-of-the-art nuclear plant design practice. TheFukushima catastrophe suggests that the means for removing the plant'sdecay heat should be diversified to include direct rejection to air tofurther harden nuclear plants against beyond-the-design basis extremeenvironmental phenomena.

BRIEF SUMMARY OF THE INVENTION

These, and other drawbacks, are remedied by the present invention, whichprovides an independent system for rejecting waste heat generated byradioactive materials within a nuclear power plant to the ambient air.

In one embodiment, the invention can be a system for removing thermalenergy generated by radioactive materials comprising: an air-cooled heatexchanger; a heat rejection closed-loop fluid circuit comprising atube-side fluid path of the air-cooled heat exchanger, a coolant fluidflowing through the heat rejection closed-loop fluid circuit, the heatrejection closed-loop fluid circuit thermally coupled to the radioactivematerials so that thermal energy generated by the radioactive materialsis transferred to the coolant fluid; and the air-cooled heat exchangercomprising a shell-side fluid path having a first air inlet, a secondair inlet and an air outlet, the first air inlet located at a firstelevation, the second air inlet located at a second elevation, and theair outlet located at a third elevation, the second elevation greaterthan the first elevation and the third elevation greater than the secondelevation, the air-cooled heat exchanger transferring thermal energyfrom the coolant fluid flowing through the tube-side fluid path to airflowing through the shell-side fluid path.

In another embodiment, the invention can be a system for removingthermal energy generated by radioactive materials comprising: anair-cooled shell-and-tube heat exchanger comprising a shell andplurality of heat exchange tubes arranged in a substantially verticalorientation within the shell, the plurality of heat exchange tubescomprising interior cavities that collectively form a tube-side fluidpath, the shell forming a shell-side fluid path that extends from an airinlet of the shell to an air outlet of the shell, the first air inletlocated at a lower elevation than the air outlet; a heat rejectionclosed-loop fluid circuit comprising the tube-side fluid path of theair-cooled heat exchanger, a coolant fluid flowing through the heatrejection closed-loop fluid circuit, the heat rejection closed-loopfluid circuit thermally coupled to the radioactive materials so thatthermal energy generated by the radioactive materials is transferred tothe coolant fluid; and the air-cooled shell-and-tube heat exchangertransferring thermal energy from the coolant fluid flowing, through thetube-side fluid path to air flowing through the shell-side fluid path.

In yet another embodiment, the invention can be a tube-and-shellair-cooled heat exchanger apparatus comprising: a shell having a shellcavity, a primary air inlet at a first elevation, a secondary air inletat a second elevation, and an air outlet at a third elevation, whereinthe second elevation is greater than the first elevation and the thirdelevation is greater than the second elevation, each of the primary airinlet, the secondary air inlet, and the air outlet forming a passagewaythrough the shell to a shell-side fluid path; and a plurality of heatexchange tubes that collectively form a tube bundle having asubstantially vertical longitudinal axis, the tube bundle located withinthe shell cavity, a tube-side fluid path comprising interior cavities ofthe plurality of heat exchange tubes.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic of a system for rejecting thermal energy generatedby radioactive waste to the ambient air according to an embodiment ofthe present invention;

FIG. 2 is a schematic of a shell-and-tube air-cooled heat exchanger thatcan be used in the system of FIG. 1 according to an embodiment of thepresent invention;

FIG. 3 is a transverse cross-section of a heat exchange tube of theshell-and-tube air-cooled heat exchanger along a finned sectionaccording to an embodiment of the present invention; and

FIG. 4 is a graph of the free cross-sectional area of the shell-sidefluid path of the shell-and-tube air-cooled heat exchanger of FIG. 2along a length of the shell-side fluid path in according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. While the invention is exemplified in FIGS.1-4 as being used to cool spent nuclear fuel that is located within aspent nuclear fuel pool, the invention is not so limited. In otherembodiments, the invention can be used to reject waste thermal energygenerated by radioactive materials to the ambient air irrespective ofthe type of radioactive materials being cooled and the type of body ofliquid in which the radioactive materials are (or previously were)immersed. In certain embodiments, the pool of liquid can be a reactorpool. In other embodiments, the radioactive materials may be waste,including spent nuclear fuel, high level radioactive waste or low levelradioactive waste, and/or non-waste.

Referring first to FIG. 1, a cooling system 1000 for rejecting thermalenergy generated by radioactive waste 20 to the ambient air 40 accordingto an embodiment of the present invention is schematically illustrated.The cooling system 1000 generally comprises an air-cooled heat exchanger100 and a heat rejection closed-loop fluid circuit 200 that thermallycouples the air-cooled heat exchanger 100 to the radioactive materials20, which are immersed in a pool of a liquid 50. As a result of thethermal coupling, thermal energy generated by the radioactive waste 20is transferred to the air-cooled heat exchanger 100 (and subsequently tothe ambient air 40). Thermal coupling of the air-cooled heat exchanger100 to the radioactive waste 20 via the heat rejection closed-loop fluidcircuit 200 can either be direct thermal coupling or indirect thermalcoupling. In the exemplified embodiment, the thermal coupling of theair-cooled heat exchanger 100 to the radioactive waste 20 via the heatrejection closed-loop fluid circuit 200 is accomplished via an indirectthermal coupling that includes an intermediate closed-loop fluid circuit300. In this embodiment, the intermediate closed-loop fluid circuit 300comprises the pool of liquid 50. In other embodiment, a pool of liquid50 may not be required and the radioactive waste may transfer itsthermal energy to a gaseous volume to which the air-cooled heatexchanger 100 is thermally coupled.

It should be noted that in certain alternate embodiments of theinvention, more than one intermediate closed-loop fluid circuit 300 canbe included in the cooling system 1000 that consecutively transferthermal energy from the radioactive materials 20 to the heat rejectionclosed-loop fluid circuit 200. In such an embodiment, only a first oneof the intermediate closed-loop fluid circuits 300 will comprise thepool of the liquid 50. Moreover, in certain other alternate embodiments,the intermediate closed-loop fluid circuit 300 can be omitted. In suchan embodiment, the heat rejection closed-loop fluid circuit 200 caninclude the pool of the liquid 50.

The cooling system 1000, in the exemplified embodiment, furthercomprises an intermediate heat exchanger 310 which, as discussed below,transfers thermal energy from the liquid 50 to a coolant fluid 101 thatflows through the heat rejection closed-loop fluid circuit 200. In theexemplified embodiment, the intermediate heat exchanger 310 is atube-and-shell heat exchanger. However, in other embodiments, theintermediate heat exchanger 310 can be a plate heat exchanger, a plateand shell heat exchanger, an adiabatic heat exchanger, a plate fin heatexchanger, and a pillow plate heat exchanger.

The system 1000 further comprises a containment structure 75, which canbe in the form of a building or other enclosure. The containmentstructure 75 provides radiation containment as would be appreciated bythose skilled in the art. In certain embodiment, the system 1000 isdesigned so that the liquid 50, which comes into direct contact with theradioactive waste 20, never exists the containment structure 75. Thus,if a leak were to occur in the intermediate closed-loop fluid circuits300, the contaminated liquid 50 would not be discharged into thesurrounding environment. Thus, in the exemplified embodiment, theintermediate heat exchanger 310 and the entirety of the intermediateclosed-loop fluid circuits 300 is located within the containmentstructure 75. Whether or not containment of the liquid 50 within thecontainment structure is required will depend on whether or not theliquid is contaminated, the type of radioactive waste 20 being cooled,and applicable regulations.

As mentioned above, radioactive materials 20 are immersed in the pool ofthe liquid 50, which in the exemplified embodiment is a spent fuel pool.Radioactive materials 20, such as spent nuclear fuel, generate asubstantial amount of heat for a considerable amount of time aftercompletion of a useful cycle in a nuclear reactor. Thus, the radioactivematerials 20 are immersed in the pool of the liquid 50 to cool theradioactive materials 20 to temperatures suitable for dry storage. Inembodiments where the radioactive materials 20 are spent nuclear fuelrods, said spent nuclear fuel rods will be supported in the pool of theliquid 50 in fuel racks located at the bottom of the pool of liquid 50and resting on the floor. Examples of suitable fuel racks are disclosedin United States Patent Application Publication No. 2008/0260088,entitled Apparatus and Method for Supporting Fuel Assemblies in anUnderwater Environment Having Lateral Access Loading, published on Oct.23, 2008, and United States Patent Application Publication No.2009/0175404, entitled Apparatus or Supporting Radioactive FuelAssemblies and Methods of Manufacturing the Same, published on Jul. 9,2009, the entireties of which are hereby incorporated by reference.

As a result of being immersed in the pool of the liquid 50, thermalenergy from the radioactive materials 20 is transferred to the pool ofthe liquid 50, thereby heating the pool of liquid 50 and cooling theradioactive materials. However, as the pool of liquid 50 heats up overtime, thermal energy must be removed from the pool of the liquid 50 tomaintain the temperature of the pool of the liquid 50 within anacceptable range so that adequate cooling of the radioactive materials20 can be continued.

The intermediate closed-loop fluid circuit 300 comprises, in operablefluid coupling, the pool of the liquid 50, a tube-side fluid path 320 ofthe intermediate heat exchanger 310, and a hydraulic pump 330. Theaforementioned components/paths of the intermediate closed-loop fluidcircuit 300 are operably and fluidly coupled together using appropriatepiping, joints and fittings as is well-known in the art to form afluid-tight closed-loop through which the liquid 50 can flow. Thehydraulic pump 330 flows the liquid 50 through the intermediateclosed-loop fluid circuit 300 as is known in the art. Of course, valvesare provided as necessary and/or desirable along the intermediateclosed-loop fluid circuit 300.

In the exemplified embodiment, the tube-side fluid path 320 of theintermediate heat exchanger 310 comprises a tube-side inlet header 321,a tube-side outlet header 322 and interior cavities 324 of the heatexchange tubes 325 of the intermediate heat exchanger 310. The shell 329of the intermediate heat exchanger 310 comprises a tube-side inlet 328for introducing heated liquid 50 into the tube-side fluid path 320 ofthe intermediate heat exchanger 310 and a tube-side outlet 331 forallowing cooled liquid 50 to exit the tube-side fluid path 320 of theintermediate heat exchanger 310.

Interior cavities 324 of the heat exchange tubes 325 fluidly couple thetube-side inlet header 321 and the tube-side outlet header 322, therebyforming the tube-side fluid path 320 of the intermediate heat exchanger310. The heat exchange tubes 325 of the intermediate heat exchanger 310are connected to an inlet tube sheet 326 and an outlet tube sheet 327 atopposite ends.

The heat rejection closed-loop fluid circuit 200 comprises, in operablefluid coupling, a shell-side fluid path 340 of the intermediate heatexchanger 310, a tube-side fluid path 110 of the air-cooled heatexchanger 100, a fluid coolant reservoir 210 and a hydraulic pump 220.The aforementioned components/paths of the heat rejection closed-loopfluid circuit 200 are operably and fluidly coupled together usingappropriate piping, joints and fittings as is well-known in the art toform a fluid-tight closed-loop through which the coolant fluid 101 canflow. The hydraulic pump 220 flows the coolant fluid 101 through theheat rejection closed-loop fluid circuit 200 as is known in the art. Ofcourse, valves are provided as necessary and/or desirable along the heatrejection closed-loop fluid circuit 200. The coolant fluid 101 can takeon a wide variety of fluids, including both liquids and gases. In oneembodiment, the coolant fluid 101 is water in liquid phase.

The tube-side fluid path 110 of the air-cooled heat exchanger 100comprises, in operable fluid coupling, a coolant fluid inlet header 111,interior cavities 112 of a plurality of heat exchange tubes 113, and acoolant fluid outlet header 114. The plurality of heat exchange tubes113 collectively form a tube bundle 115 that extends along asubstantially vertical longitudinal axis A-A. Furthermore, each of theheat exchange tubes 113 of the air-cooled heat exchanger 100 arearranged in a substantially vertical orientation. The tube bundle 115further comprises a top tube sheet 116 and a bottom tube sheet 117. Theheat exchange tubes 113 of the air-cooled heat exchanger 100 areconnected to and extend between the top tube sheet 116 and the bottomtube sheet 117.

The air cooled heat exchanger 100 further comprises a shell 118 thatforms a shell cavity 119. The tube bundle 115 is positioned within theshell cavity 119. The air cooled heat exchanger 100 further comprises aprimary air inlet 120, a secondary air inlet 121 and an air outlet 122.Each of the primary air inlet 120, the secondary air inlet 121 and theair outlet 122 form passageway through the shell 118 from the shellcavity 119 to the ambient air 40. As such, ambient air 40 can flow intoand/or out of the shell cavity 119 via the primary air inlet 120, thesecondary air inlet 121 and the air outlet 122 so that thermal energycan be convectively removed from the exterior surfaces of the heatexchange tubes 113. More specifically, cool ambient air 40 flows intothe shell cavity 119 via the primary air inlet 120 and the secondary airinlet 121 while warmed ambient air 40 flows out of the shell cavity 119via the air outlet 122. As can be seen, the primary air inlet 120 islocated a first elevation E1, the secondary air outlet 121 is located ata second elevation E2 and the air outlet 122 is located at a thirdelevation E3. The second elevation E2 is greater than the firstelevation E1. The third elevation E3 is greater than the secondelevation E2. In one embodiment, the primary air inlet 120 has a greatereffective cross-sectional area than the secondary air outlet 121. Theinvention, however, is not so limited in all embodiments. While notillustrated in FIG. 1, the air-cooled heat exchanger 100 can comprise ablower (see FIG. 2) to induce air flow through the shell-side fluid path123 of the shell cavity 119. Conceptually, the shell-side fluid path 123of the air-cooled heat exchanger 100 is the remaining free volume of theshell cavity 119 through which the ambient air 40 can flow (after thetube bundle 115 and other components are positioned therein).

In other embodiments of the present invention, the air cooled heatexchanger 100 may comprise a plurality of secondary air inlets 121. Insuch instances, the plurality of secondary air inlets 121 may be atvarying elevations between the first elevation E1 and the thirdelevation E3. Stated another way, in such embodiments the plurality ofsecondary air inlets 121 may be at a plurality of different elevationsbetween the first elevation E1 of the primary air inlet 120 and thethird elevation E3 of the air outlet 122. In further embodiments, thesecondary air inlet 121 may be omitted.

In the exemplified embodiment, the air-cooled heat exchanger 100 is avertical single tube pass counter-current heat exchanger. However, incertain embodiment, multiple pass heat exchangers can be used for eitherthe air-cooled heat exchanger 100 and/or the intermediate heat exchanger310. The heat exchange tubes 325 of the intermediate heat exchanger 310and the heat exchange tubes 113 of the air-cooled heat exchanger 100 aremade of made of a highly thermally conductive and corrosion resistantmaterial. Suitable materials include aluminum, copper, and aluminumalloys.

During operation of the system, the hydraulic pumps 330 and 210 areactivated. Activation of the hydraulic pump 330 flows liquid 50 throughthe intermediate closed-loop fluid circuit 300 while activation of thehydraulic pump 220 flows coolant fluid 101 through the heat rejectionclosed-loop fluid circuit 200. As discussed above, the thermal energygenerated by the radioactive waste 20 is initially transferred to theliquid 50 while in the pool. This heated liquid 50 flows from the pooland into the tube-side fluid path 320 of the intermediate heat exchanger310. Simultaneously, the coolant fluid 101 (which at this stage has beencooled by the air-cooled heat exchanger 100) flows through theshell-side fluid path 340 of the intermediate heat exchanger 310. As theheated liquid 50 flows through the tube-side fluid path 320 of theintermediate heat exchanger 310, thermal energy is transferred from theheated liquid 50 to the cool coolant fluid 101 that is flowing thoughthe shell-side fluid path 340 of the intermediate heat exchanger 310.The cooled liquid 50 then exits tube-side path 320 of the intermediateheat exchanger 310 and is returned back to the pool for further coolingof the radioactive materials 20 where it is again heated up and thecycle continues.

The heated coolant fluid 101 (which has absorbed the thermal energy fromthe heated liquid 50) exits the shell-side path 340 of the intermediateheat exchanger 310 and flows into the top header 111 of the air-cooledheat exchanger 100 where it is then distributed to the interior cavities112 of the plurality of heat exchange tubes 113. The heated coolantfluid 101 flows downward through the plurality of heat exchange tubes113. As the heated coolant fluid 101 flows through the plurality of heatexchange tubes 113, thermal energy from the heated coolant fluid 101 istransferred to ambient air 40 that is flowing through the shell-sidefluid path 123 of the air cooled-heat exchanger 100. The ambient air 40enters the primary air inlet 120 as cool air. As thermal energy from thecoolant fluid 101 is transferred to this cool ambient air 40 within theshell-side fluid path 123, the ambient air 40 becomes warmed and risesnaturally within the shell-side fluid path 123 and exits the air-cooledheat exchanger 100 via the air outlet 122 as heated air. Additionally,as the warmed ambient air 40 rises within the shell-side fluid path 123,additional cool ambient air 40 is drawn into the shell-side fluid path123 via the second air inlet 121. The second air inlet 121 also servesas a backup to the primary air inlet 120 in the event that the site isflooded and the primary inlet 120 becomes submerged in water.

Referring now to FIG. 2, a tube-and-shell air-cooled heat exchangerapparatus 500A that is particularly useful as the air-cooled heatexchanger 100 for the cooling system 1000 is illustrated. Thetube-and-shell air-cooled heat exchanger apparatus 500A will bedescribed with the understanding that those parts of the tube-and-shellair-cooled heat exchanger apparatus 500A that correspond to theair-cooled hate exchanger 100 will be given like reference numbers withthe addition of an “A” suffix.

The tube-and-shell air-cooled heat exchanger apparatus 500A generallycomprises a tube-and-shell air-cooled heat exchanger 100A and a shroud160A. The tube-and-shell air-cooled heat exchanger 100A comprises a tubebundle 115A and a shell 118A. The shroud 160A comprises a shroud cavity161A. The shell 118A comprises a shell cavity 119A. The tube bundle 115Ais positioned within the shell cavity 119A and supported therein asubstantially vertical orientation along substantially vertical axisA-A. The tube-and-shell air-cooled heat exchanger 100A is positionedwithin the shroud cavity 161A and supported therein in a substantiallyvertical orientation along vertical axis A-A. In certain embodiments,the shroud 160A may be omitted. In certain other embodiments, the shroud160A may be considered the shell of the tube-and-shell air-cooled heatexchanger apparatus 500A while the shell 118A is omitted.

The tube-and-shell air-cooled heat exchanger apparatus 500A comprises ashell-side fluid path 123A and a tube-side fluid path 110A. As mentionedabove, the shell-side fluid path 123A can be conceptualized as the freevolume of the shell cavity 119 that remains after the tube bundle 115A(and other components) is positioned therein. The tube-side fluid path110A comprises the interior cavities 112A of the plurality of heatexchange tubes 113A along with the coolant fluid inlet header 111A andthe coolant fluid outlet header 114A. The coolant 101 flows through thetube-side fluid path 110A while the ambient air flows through theshell-side fluid path 123A as discussed above for FIG. 1 to effectuatetransfer of thermal energy from the coolant fluid 101 to the ambient air40.

The tube-and-shell air-cooled heat exchanger apparatus 500A comprises aprimary air inlet 120A, a secondary air inlet 121A, and an air outlet122A. The primary air inlet 120A and the secondary air inlet 122A formpassageways from the ambient air 40A outside of the shroud 160A into theshell-side fluid path 123A, thereby allowing cool air to enter theshell-side fluid path 123A from outside of the shroud 160A. The airoutlet 122A forms a passageway from the shell-side fluid path 123A to ashroud outlet plenum 162A that circumferentially surrounds a top portionof the shell 118A. A chimney 163A is provided on the shroud 160A thatforms a passageway from the shroud outlet plenum 162A to the ambient air40A outside of the shroud 160A. Thus, as warmed ambient air 40A exitsthe shell-side fluid path 123A via the air outlet 122A, the warmedambient air 40A will flow into the shroud outlet plenum 162A, risetherein, and exit the shroud via the passageway of the chimney 163A. Inorder to induce greater flow of ambient air through the shell-side fluidpath 123A of the tube-and-shell air-cooled heat exchanger apparatus500A, a blower 170A is provided in the chimney 163A. In otherembodiments, the blower 170A may be positioned at other suitablelocations.

Each of the primary air inlet 120A, the secondary air inlet 121A, andthe air outlet 122A extend through the shell 118A and are substantiallyhorizontal. The primary air inlet 120A is formed by one or more conduitsthat extend through the shroud 160A and to the shell 118A so that all ofthe incoming cool air flows into the shell-side fluid path 123A and notinto the shroud cavity 161A. Similarly, the secondary air inlet 121A isformed by one or more conduits that extend through the shroud 160A andto the shell 118A so that all of the incoming cool air flows into theshell-side fluid path 123A and not into the shroud cavity 161A.

The primary air inlet 120A is located a first elevation E1, thesecondary air outlet 121A is located at a second elevation E2 and theair outlet 122A is located at a third elevation E3. The second elevationE2 is greater than the first elevation E1. The third elevation E3 isgreater than the second elevation E2. In one embodiment, the primary airinlet 120A has a greater effective cross-sectional area than thesecondary air outlet 121A.

The plurality of heat exchange tubes 113A are discontinuously finnedtubes. In other words, each of the plurality of heat exchange tubes 113Acomprise axial sections that include fins 180A (FIG. 3) and axialsections that are free of any fins. In certain alternate embodiments ofthe invention, a first subset of the heat exchange tubes 113A may bediscontinuously finned tubes, a second subset of the heat exchange tubes113A may be continuously finned along their length, and a third subsetof the heat exchange tubes 113A may be free of fins along their entirelength.

In the exemplified embodiment, the plurality of heat exchange tubes 113Acollectively form the tube bundle 115A. Due their discontinuously finnednature, the tube bundle 115 a comprises finned tube sections 151A, 153Aand non-finned tube sections 150A, 152A, 154A. The finned tube sections151A, 153A and the non-finned tube sections 150A, 152A, 154A are inaxial alignment and arranged in an alternating manner. In the finnedtube sections 151A, 153 A of the tube bundle 115A, each of the heatexchange tubes 113A comprise fins 180A that increase thermal energytransfer from the coolant fluid 101A to the ambient air 40A byincreasing the outer surface area of the tubes 113A. In the non-finnedtube sections 150A, 152A, 154A, the plurality of heat exchange tubes113A are free of any fins.

As can be seen in FIG. 2, in the exemplified embodiment, the non-finnedtube sections 150A, 152A, 154A are transversely aligned with the primaryair inlet 120A, the secondary air inlet 121A, and the air outlet 122Arespectively. By aligning each of the primary air inlet 120A, thesecondary air inlet 121A, and the air outlet 122A with one of thenon-finned tube sections 150A, 152A, 154A, ambient air 40A can enter andexit the tube bundle 115A more effectively. Stated simply, by omitting(or substantially reducing the number of) the fins in these sections150A, 152A, 154A, the impedance effect that the fins have on thecross-flow of the ambient air is eliminated and/or minimized. Thus, airflow through the shell-side path 123A is increased. Furthermore, thecreation and arrangement of the tinned tube sections 151A, 153A and thenon-tinned tube sections 150A, 152A, 154A on the tube bundle 115A (asdiscussed above) can create a venturi effect at the secondary air inlet121A (and potentially at the primary air inlet 120A).

Referring to FIGS. 2 and 4 concurrently, it can be seen that providingfins 180A on the finned tube sections 151A, 153A effectively reduces thefree transverse cross-sectional area of the shell-side path 123A becausethe fins 180A occupy additional space of the shell cavity 119A. Thus,from the perspective of the shell-side fluid path 123A, the finned tubesections 151A, 153A create a reduced cross-sectional area, which can beconsidered a venturi restriction. As a result of the finned section153A, which is located at an elevation between the secondary air inlet121A and the air outlet 122A, a venturi is formed that assists indrawings additional cool ambient air 40A into the secondary air inlet121A. Thus, in the exemplified embodiment, the venturi is created by thefins 180A of the plurality of heat exchange tubes 113A. Each of the fins180A of the plurality of heat exchange tubes 113A comprise opposingsurfaces that extent substantially parallel to the substantiallyvertical axis A-A.

The shell-side fluid path 123A comprises a first venturi located at anelevation between the primary air inlet 120A and the secondary air inlet121A. Furthermore, the shell-side fluid path 123A comprises a secondventuri located at an elevation between the secondary air inlet 121A andthe air outlet 122A. As graphically illustrated in FIG. 4, theshell-side fluid path 123A comprises a first free transversecross-sectional area at the second elevation (i.e. at the secondary airinlet 121A) and a second free transverse cross-sectional area at anelevation between the secondary air inlet 121A and the air outlet 122A,wherein the second free transverse cross-sectional area is less than thefirst free transverse cross-sectional area. Moreover, the shell-sidefluid path 123A comprises a third free transverse cross-sectional areaat the third elevation (i.e., at the air outlet 122A), wherein the thirdfree transverse cross-sectional area is greater than the second freetransverse cross-sectional area.

In embodiments of the invention where the focus is on existence of aventuri being created in the shell-side fluid path 123A, the venturi canbe created in additional ways, such as for example reducing thetransverse cross-section of the shell 119A or adding additional flowbarriers. In certain other embodiments, a venturi can be created bysimply adding more or thicker fins to the desired area of the tubebundle.

Referring now to FIG. 3, a transverse cross-section of one of the heatexchange tubes 113A taken along one of the finned tube sections 151A,153 is exemplified. The heat exchange tubes 113A comprise a plurality offins 180A extending from a tube body 181A. The fins 180A can be formedby extruding a set of axial spines that give the tube 113A a “starburst” cross section. The height of the find 180A is selected to accordwith the layout pitch of the tube bundle 115A such that the fins 180Aprovide a complete cross sectional coverage in the tube bundle 115A soas to promote maximum contact between the turbinated air and the finsurfaces. A candidate shape of the star burst for the square layoutpitch is shown in FIG. 3. Of course, any number of fin arrangements andpatterns can be used in other embodiments of the invention.

The design of the tube-and-shell air-cooled heat exchanger apparatus500A described above has several parameters for modification to maximizeits heat rejection capability for a specific application. The availableparameters include tube I.D., number of fins per tube and size/shape ofeach fin, tube layout pitch, height of the tube bundle, in-tube flowvelocity (by using the appropriate size pump) and air flow velocity (byselecting the appropriately sized blower). By an adroit selection of theabove design parameters, it is possible to achieve the overall heattransfer coefficient for the bundle in excess of 10 Btu/hr-sq ft-deg F.Scoping calculations show that a 12 ft diameter, 20 ft tall heat bundlecan remove as much as 5858 kW from contaminated water @ 140 deg. F.Multiple units can be arrayed in parallel to increase the heat removalcapacity to the desired level.

As used throughout, ranges are used as shorthand for describing each andevery value that is within the range. Any value within the range can beselected as the terminus of the range. In addition, all references citedherein are hereby incorporated by referenced in their entireties. In theevent of a conflict in a definition in the present disclosure and thatof a cited reference, the present disclosure controls.

While the invention has been described with respect to specific examplesincluding presently preferred modes of carrying out the invention, thoseskilled in the art will appreciate that there are numerous variationsand permutations of the above described systems and techniques. It is tobe understood that other embodiments may be utilized and structural andfunctional modifications may be made without departing from the scope ofthe present invention. Thus, the spirit and scope of the inventionshould be construed broadly as set forth in the appended claims.

What is claimed is:
 1. A system for removing thermal energy generated byradioactive materials comprising: an air-cooled heat exchanger; a heatrejection closed-loop fluid circuit comprising a tube-side fluid path ofthe air-cooled heat exchanger, a coolant fluid flowing through the heatrejection closed-loop fluid circuit, the heat rejection closed-loopfluid circuit thermally coupled to the radioactive materials so thatthermal energy generated by the radioactive materials is transferred tothe coolant fluid; and the air-cooled heat exchanger comprising ashell-side fluid path having a first air inlet, a second air inlet andan air outlet, the first air inlet located at a first elevation, thesecond air inlet located at a second elevation, and the air outletlocated at a third elevation, the second elevation greater than thefirst elevation and the third elevation greater than the secondelevation, the air-cooled heat exchanger transferring thermal energyfrom the coolant fluid flowing through the tube-side fluid path to airflowing through the shell-side fluid path; the tube-side fluid pathcomprising internal cavities of a plurality of heat exchange tubes, theplurality of heat exchange tubes located within the shell-side fluidpath; wherein the shell-side fluid path comprises a first venturilocated at an elevation between the second air inlet and the air outlet,the first venturi created by fins of the plurality of heat exchangetubes; wherein the shell-side fluid path comprises a second venturilocated at an elevation between the first air inlet and the second airinlet, the second venturi created by fins of the plurality of heatexchange tubes; wherein the fins are discontinuous in structure suchthat the plurality of heat exchange tubes between the first venturi andsecond venturi at the second air inlet do not have fins.
 2. The systemof claim 1 wherein the plurality of heat exchange tubes form a tubebundle having a longitudinal axis, and wherein each of the fins of theplurality of heat exchange tubes comprise opposing surfaces that extendsubstantially parallel to the longitudinal axis.
 3. The system of claim1 wherein the shell-side fluid path comprises a first free transversecross-sectional area at the second elevation and a second freetransverse cross-sectional area at an elevation between the second airinlet and the air outlet, the second free transverse cross-sectionalarea being less than the first free transverse cross-sectional area. 4.The system of claim 3 wherein the shell-side fluid path comprises athird free transverse cross-sectional area at the third elevation, thethird free transverse cross-sectional area being greater than the secondfree transverse cross-sectional area.
 5. The system of claim 1 furthercomprising: an intermediate heat exchanger; an intermediate closed-loopfluid circuit comprising, in operable fluid coupling, a pool of a liquidand a first fluid path of the intermediate heat exchanger, theradioactive materials immersed in the pool of the liquid, the liquidflowing through the intermediate closed-loop fluid circuit; and the heatrejection closed-loop fluid circuit further comprising a second fluidpath of the intermediate heat exchanger, the intermediate heat exchangertransferring thermal energy from the liquid flowing through the firstfluid path to the coolant fluid flowing through the second fluid path.6. The system of claim 5 wherein the pool of the liquid and theintermediate heat exchanger are contained within a containmentstructure.
 7. The system of claim 1, wherein the plurality of heatexchange tubes are arranged in a substantially vertical orientation. 8.The system of claim 7 wherein the plurality of heat exchange tubescollectively form a tube bundle that extends along a longitudinal axis,and the tube bundle comprising finned tube sections and a non-finnedtube section arranged in axial alignment, the second air inlettransversely aligned with the non-finned tube section between the finnedtube sections.
 9. The system of claim 8 wherein the finned tube sectionsand the non-finned tube section alternate along the longitudinal axis.10. The system of claim 8 further comprising a plurality of thenon-finned tube sections, each of the first air inlet, the second airinlet and the air outlet transversely aligned with one of the non-finnedtube sections.
 11. The system of claim 8 further comprising: theair-cooled heat exchanger comprising a top tube sheet and a bottom tubesheet, the plurality of heat exchange tubes extending from the top tubesheet to the bottom tube sheet, the first air inlet located adjacent thebottom tube sheet and the air outlet located adjacent the top tubesheet; and the tube-side fluid path of the air-cooled heat exchangercomprising a coolant fluid inlet header and a coolant fluid outletheader, the internal cavities of the plurality of heat exchange tubesforming passageways between the coolant fluid inlet header and thecoolant fluid outlet header.
 12. The system of claim 1 wherein theair-cooled heat exchanger comprises a shell, each of the first airinlet, the second air inlet and the air outlet formed in the shell. 13.The system of claim 12 further comprising: a shroud forming a shroudcavity, the air-cooled heat exchanger located within the shroud cavity,the shroud cavity comprising a shroud outlet plenum circumferentiallysurrounding the air-cooled heat exchanger, the air outlet of the shelllocated within the shroud outlet plenum; and a chimney forming apassageway from the shroud outlet plenum to an ambient environment. 14.The system of claim 1 further comprising a blower for inducing air flowthrough the shell-side fluid path.
 15. A system for removing thermalenergy generated by radioactive materials comprising: an air-cooledshell-and-tube heat exchanger comprising a shell and plurality of heatexchange tubes arranged in a substantially vertical orientation withinthe shell, the plurality of heat exchange tubes comprising interiorcavities that collectively form a tube-side fluid path, the shellforming a shell-side fluid path that extends from an air inlet of theshell to an air outlet of the shell, the first air inlet located at alower elevation than the air outlet and the plurality of heat exchangetubes located within the shell-side fluid path; the shell comprising asecond air inlet located at an elevation between the first air inlet andthe air outlet; a heat rejection closed-loop fluid circuit comprisingthe tube-side fluid path of the air-cooled heat exchanger, a coolantfluid flowing through the heat rejection closed-loop fluid circuit, theheat rejection closed-loop fluid circuit thermally coupled to theradioactive materials so that thermal energy generated by theradioactive materials is transferred to the coolant fluid; and theair-cooled shell-and-tube heat exchanger transferring thermal energyfrom the coolant fluid flowing through the tube-side fluid path to airflowing through the shell-side fluid path; wherein the shell-side fluidpath comprises a first venturi located at an elevation between thesecond air inlet and the air outlet, the first venturi created by finsof the plurality of heat exchange tubes; wherein the shell-side fluidpath comprises a second venturi located at an elevation between thefirst air inlet and the second air inlet, the second venturi created byfins of the plurality of heat exchange tubes; wherein the fins arediscontinuous in structure such that the plurality of heat exchangetubes between the first venturi and second venturi at the second airinlet do not have fins.
 16. The system of claim 15 further comprising apool of a liquid, the radioactive materials immersed in the pool of theliquid, wherein thermal energy generated by the radioactive materials istransferred to the liquid of the pool prior to being transferred to thecoolant fluid.
 17. The system of claim 15 further comprising: a shroudforming a shroud cavity, the shell of the shell-and-tube air-cooled heatexchanger located within the shroud cavity, the shroud cavity comprisinga shroud outlet plenum circumferentially surrounding the shell-and-tubeair-cooled heat exchanger, the air outlet of the shell located withinthe shroud outlet plenum; and a chimney forming a passageway from theshroud outlet plenum to an ambient environment.
 18. The system of claim15 further comprising a blower for inducing air flow through theshell-side fluid path.
 19. The system of claim 15 wherein the pluralityof heat exchange tubes collectively form a tube bundle that extendsalong a longitudinal axis, and the tube bundle comprising finned tubesections and non-finned tube sections arranged in alternating axialalignment.